Accurate computational studiesof catalytic reaction mechanismsand kinetics
Başlık çevirisi mevcut değil.
- Tez No: 760701
- Danışmanlar: PROF. JEREMY N. HARVEY
- Tez Türü: Doktora
- Konular: Kimya, Chemistry
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2021
- Dil: İngilizce
- Üniversite: Katholieke Universiteit Leuven (Catholic University of Leuven)
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 155
Özet
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Özet (Çeviri)
Studies on catalysis using computational chemistry have the potential to reveal information on mechanism and reactivity that is less easily obtained from experiment. Quantitative analysis of catalytic processes and their mechanisms can provide the insight needed to generate improved catalysts, and computational chemistry contributes increasingly to this goal in part thanks to the ever-increasing computational power, but also to improved theoretical understanding. Catalysis has many types, and while they are all potentially of great interest, this thesis focuses on two important types: homogenous catalysis with noble metal complexes and organocatalysis. In line with that, our aim for this thesis was to quantitatively analyze a variety of reaction mechanisms that include noble metal catalysis and organocatalysis using density functional theory (DFT) and reaction path optimization using the growing string method. To achieve this goal, in all of the projects, we investigated the full catalytic cycles and tried to compare our results with kinetic data in cases where it was available. Also, the important single reaction steps such as transmetallation steps in the first two projects and the reduction steps in the last project were independently investigated as part of the possible bottlenecks of the studies. Chapter 1 includes a concise introduction to the chemical concepts, catalysis and origins of life, that are fundamental for the research projects that were performed in the thesis. For both of the topics, the modern status of computational and experimental studies were reported. Chapter 2 comprises the relevant theoretical background for the computational methods that have been used throughout the studies. Chapter 3 is about the first project of this thesis, a mechanistic study conducted on the entire catalytic cycle of Suzuki-Miyaura cross-coupling, which refers to very recent experimental data relating to an unexpected discovery of a pre-transmetallation intermediate. Our calculations reported here confirm the overall stability of the newly detected intermediate. Then, the study was focused on the transmetallation step. Two possible hypotheses about the transmetallation process were investigated and one of the suggestions that included a transition state in which the departing boron atom had significant divalent character was ruled out. In addition to these aspects, our work included a method to calculate the free energy change of reaction steps in which the reactant base (a solid) was involved. This yields a more realistic treatment of such reactions where a solid base plays a role. Chapter 4 is again related to Suzuki-Miyaura cross-coupling; here our mechanistic study addressed a recently reported“base-free”coupling reaction. One focus of our work was to identify the species that in practice acts as the base. In addition to that, our calculations show that the first few turnovers of the catalytic cycle most likely involved different species than the subsequent turnovers, in vi which the arylboronic acid moiety is recycled. Chapter 5 is a study of organocatalysis, relating to a mechanistic hypothesis for prebiotic amino acid synthesis. The mechanism had been proposed by other authors as a possible explanation for the modern amino acidcodon correlation with the possible help of dinucleotides as ancient catalysts. Our calculations provided insight with a suggestion of a new reagent to the mechanistic scheme and argued that the overall hypothesis is broadly plausible. Chapter 6 is about the overall conclusions regarding the studies done as part of the thesis
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